Effective number of codons (abbreviated as ENC or Nc) is a measure to study the state of codon usage biases in genes and genomes.[1] The way that ENC is computed has obvious similarities to the computation of effective population size in population genetics.[2] Although it is easy to compute ENC values, it has been shown that this measure is one of the best measures to show codon usage bias.[3]
Since the original suggestion of the ENC, several investigators have tried to improve the method, [4][5] but it seems that there is much room to improve this measure[6][7][8][9][10][11].